EG, sorry to hear of the left channel problem, which I can't shed any light on.
Re your and MGlenn's observations of improved sound with both sets of cables connected, I suspect that the reason it is not discussed more frequently is that it is specific to your equipment.
I think that MGlenn's observation that significant sound comes through even when unconnected inputs are selected is key. That indicates crosstalk between inputs within the A21, and is most likely an unintended (and non-ideal) characteristic of the design. For whatever reason, though, it apparently happens to be synergistic with the A21's overall sonic characteristics and/or the characteristics of the rest of your systems.
Best regards,
-- Al
Re your and MGlenn's observations of improved sound with both sets of cables connected, I suspect that the reason it is not discussed more frequently is that it is specific to your equipment.
I think that MGlenn's observation that significant sound comes through even when unconnected inputs are selected is key. That indicates crosstalk between inputs within the A21, and is most likely an unintended (and non-ideal) characteristic of the design. For whatever reason, though, it apparently happens to be synergistic with the A21's overall sonic characteristics and/or the characteristics of the rest of your systems.
Best regards,
-- Al